Question

what is called ionisation enathlpy

Answer 1

The energy required to remove an electron from a neutral isolated gaseous atom and convert it into a positively charged gaseous ion is called ionisation energy .. ☺ ☺

Answer 2

ionization enthalpy is the amount of energy required to remove the outermost electron from an isolated gaseous atom it is also sometimes termed as ionization potential ionization energy.
it depends on second factors such as

atomic size
screening effect
charge of ion etc